Closed loop thermal energy distribution systems circulate an energy transfer medium to heat or cool buildings or equipment. Heat is absorbed or dissipated to or from the medium to heat or cool loads that are in thermal contact with the closed loop water circulation system.
Prior art water circulation control systems have generally focused on chiller/boiler temperature and pressure supply control and not building dynamic load. The prior art systems generally relied on pressure measurements to control the system volume flow by inducing sufficient flow through pressure supplied by the pump in the system. The pressure in the system however is not directly related to the cooling load required by the building.
The pressure in prior art systems is generally controlled using a fixed speed pump in combination with valving, or through the use of a variable speed pump motor in combination with valving, such as a centrifugal pump with a variable speed motor and a balancing valve. Pressure control of a system is not possible when there are no valves present in the system, or may be difficult when a water bypass is present, allowing for unrestricted flow of water in the system.
There is a need for a control method for a water circulation system that is based upon actual heating or cooling load on the system.